The present invention relates to an optical communication module, a mounting method thereof and an electronic apparatus, and more particularly relates to an optical communication module for use in system for transmitting signals with use of optical fibers, particularly in digital communication system enabling high-speed transmission such as IEEE (Institute of Electrical and Electronics Engineers) 1394 and USB (Universal Serial Bus) 2, a mounting method thereof, and an electronic apparatus.
As a conventional first optical communication module, there is one disclosed in Japanese Patent Laid-Open Publication No. 2000-34707. This optical communication module includes, as shown in FIG. 21, a ferrule holder 105 having a reception ferrule holder 105b and a transmission ferrule holder 105c formed integrally. The reception ferrule holder 105b secures an optical plug (unshown), which is to be inserted into an optical plug detachable port 101c, to a specified position for establishing optical connection to a light emitting device assembly. Also, the transmission ferrule holder 105c secures an optical plug (unshown), which is to be inserted into an optical plug detachable port 101b, to a specified position for establishing optical connection to a light receiving device assembly. In FIG. 21, there are shown: an electric circuit board 107 on which a driving electric circuit for transmission and an electric circuit for reception are mounted; a casing 101; a light receiving device 103; a light emitting device 104; and an electric connection pin 108 as a means for electrically connecting an electric circuit mounted on the electric circuit board 107 to an external electric circuit.
As a conventional second optical communication module, there is one for use in communication system employing ATM (Asynchronous Transfer Mode) and IEEE1394b. FIG. 22A is a top view showing the optical communication module, while FIG. 22B is a side view showing the optical communication module. In FIGS. 22A and 22B, a mold-packaged light emitting device 203 and a light receiving device 204 are mounted on a holder 202 in which a transmission connector and a reception connector enabling attachment and detachment of an optical plug 201 are formed integrally. The holder 202 is disposed on an electric circuit board 207 on which there are mounted an integrated circuit portion 205 for driving the light emitting device and an integrated circuit portion 206 for processing signal from the light receiving device. In FIGS. 22A and 22B, reference numeral 208 denotes a connection terminal as a means for electrically connecting an electric circuit mounted on the electric circuit board 207 to an external electric circuit.
Also, as a conventional third optical communication module, there is one disclosed in Japanese Patent Laid-Open Publication No. 2001-116958. In the optical communication module, as shown in FIG. 23, an optical module mainframe 303 is provided with a receptacle portion 302 that enables attachment and detachment of an optical connector 301. Also, on the lower side of the optical module mainframe 303, there is provided an electric terminal 304 allowing the mainframe to be mounted on a mounting board 306. The electric terminal 304 is disposed so as to correspond to a land 308 of the mounting board 306. Further, on the lower side of the optical module mainframe 303, there is provided a stud portion 305. On the mounting board 306, there is formed a fixing hole 307 engaging with the stud portion 305, and by the stud portion 305, the optical module mainframe 303 is positioned on the mounting board 306. In this optical communication module structure, after the stud portion 305 of the optical module mainframe 303 is engaged with the fixing hole 307 of the mounting board 306, solder between the electric terminal 304 and the land 308 is melted so that the optical module mainframe 303 is reflow-mounted on the mounting board 306.
In the above first and second optical communication modules, electric connection to a mounting board is achieved by inserting an input/output terminal provided on the optical communication module into a through hole provided on the mounting board, and conducting soldering or solder-flowing. Also, in the third optical communication module, electric connection is achieved by providing the mounting board 306 with the land 308 in a position corresponding to the position of the electric terminal 304 of the optical communication module, and melting the solder between the electric terminal 304 and the land 308 by reflowing.
In each of the above first to third optical communication modules, electric connection is achieved through melting of the solder, which requires a heat processing step to melt solder in the process of soldering, flowing and reflowing. The heat processing causes a problem that the thermal stress is applied to internal optical devices and electric circuits such as optical device driving circuits and signal processing circuits in the optical communication module, thereby causing damages and failure. Further, in a soldering step with use of a soldering-gun, there is the possibility that in the soldering operation, static electrical charges cause destruction of the internal optical devices and the electric circuits such as optical device driving circuits and signal processing circuits, which requires some measure to prevent electrostatic destruction, and therefore makes smooth establishment of electric connection difficult.
Also in the case of the second optical communication module, when the optical communication module is mounted on the board, mechanical connection and electric connection are established only by soldering the connection terminal 208 as an input/output electric terminal and as a fixing terminal. Consequently, stress generated in attaching and detaching the optical plug 201 is imposed on the connection terminal 208, so that a failure due to imperfect contact of a soldered portion may occur. Further in the case of the first and third optical communication modules, stress generated in attaching and detaching the optical plug tends to be directly imposed on the soldered terminal, thereby causing a failure due to imperfect contact of the soldered portion.
Further in recent years, use of laser diode as an internal light emitting device of optical communication modules is frequent, and so it is considered that the products incorporating the optical communication module may suffer failure of the optical communication module relating to the life of the laser diode. In the case of the above-stated conventional first to third optical communication modules, electric connection is established by soldering. Consequently, when failure of the optical communication module occurs and replacement of the optical communication module is required, re-melting of solder is necessary, which makes the replacement operation difficult. Also, in the step of re-melting the solder, thermal stress is also posed on peripheral circuits, which may cause failure of those peripheral circuits.